Method and apparatus for cleaning metal strip



March 1l, 1941. J. F. FERM ErAL METHOD AND APPARATUS FOR CLEANING METAL STRIP Filed Aug. 1o, 193e Patented Mar. 1l, 1941 UNITED sTATEs METHOD AND APPARATUS FOR CLEANING METAL STRIP John F. Ferm and Edward William Hopper, Midland, Pa., assignors to Pittsburgh Crucible Steel Company, Pittsburgh, Pa., a corporation of Pennsylvania Application August 10, 1938, Serial No. 224,100

2 Claims.

This invention relates to method and apparatus for cleaning strip metal, such as tin-coated steel strip.

In any process of tin-coating strip steel, the strip -must be cleaned at various stages ,of the procedure.' Of particular importance is the iinal cleaning of the coated strip following the treat- Y ment which imparts a bright, mirror-like nish thereto. This mirror nish may be applied, for example, to the matte coating obtained by electrodeposition, by passing the strip first through a hot oil bath of appropriate temperature and characteristics, such as palm oil, and thence through a cool oil bath,ltheformer to fuse the coating to a bright surface and the latter to harden. the coating so brightened.

On emerging from the latter bath the excess oil adhering to the strip may be removed mechanically, by passing the strip between a pair of rolls of rubber or the like rotating under compression, so-called squeegee rolls. Other agencies must be employed thereafter to remove the residual oil and other surface contaminations. Attempts to remove these contaminations by means of a cleansing spray or by a condensation of vapor 4on the strip, have proved unsatisfactory or ineiective. Also the known arrangements for cleaning by immersion in liquid 'solvents are unsatisfactory.

Heretofore the latter practice has been carried out by merely feeding the strip progressively i through several separate tanks of a cleaner liquid, such as carbon tetrachloride. With this procedure the cleaner liquid in the tank rst encountered by the strip soon becomes so contaminated with the oil, etc., that cleaning action in this tank practically ceases, in consequence of which the second' tank of the series is then quickly rendered equally contaminated, and so on for each succeeding tank until the strip undergoes substantially no cleaning inpassing through all of the tanks. The system, therefore, cleans effectively only for a short time after the tanks have been freshly lled with cleaner liquid, the cleaning action decreasing progressively thereafter until the tanks'are refilled. As a result the cleaned strip is not of uniform quality but varies from time to time in cleanliness and appearance in vaccordance with the condition of the baths.

The present invention overcomes the above noted and other defects by a novel construction.

and arrangement of cleaning baths employing a solvent liquid, and by a novel method of operating the same. According to the invention the strip to be cleaned is fed progressively through a succession of baths containing a cleaning liquid,

and a dow of the liquid established in the opposite direction between the baths, the baths being suitably interconnected for this purpose and cleaning liquid withdrawn, preferably contin- 5 uously, from the first bath traversed by the strip. and, after purification, returned to the tank last traversed Iby the strip.

In this way the first bath traversed by the strip removes most ofthe oil, etc. from the strip, and hence becomes most contaminated, the strip thereafter traversing progressively cleaner baths as the strip itself becomes progressively cleaner.

The system is, therefore, highly eilicient both as to the required additions of purified cleaner and as to the uniformly high degree of cleanliness imparted to the strip.

After the strip has been cleaned in the manner aforesaid it is passed between squeegee rolls for mechanically removing as much of the cleaning liquid adhering thereto as possible, following which it is passed through an evaporator of novel construction in accordance with a feature of the invention, for drying the strip.

In the drawing:

Fig. l shows schematically a preferred'modincation of a strip metal cleaning system in accordance with the invention; whilel Fig. 2 is a section at 2-2 of Fig. l showing the above mentioned novel details of the evaporator.

Referring to the drawing, there are shown four cleaning baths I to 4 inclusive, arranged in suc-l cession and contained in tanks 5, 6, provided with partitions 8, 9 respectively for separating the baths I, 2 and 3, 4 respectively. 'I'he metal strip 35 VIll to be cleaned, such as brightened, tin-coated strip steel, is passed between squeegee rolls- Il and thence into bath I and under a roll I2 immersed therein. The strip then passes from bath I between a-pair of felt members I3 or the like 40 disposed -in an orifice of partition 8; thence` into bath 2 and under roll I4 therein; thence out of .bath 2 over roll I5 and into bath 3 and under roll I6 immersed therein; thence out of bath 3 between a pair of felt or like members I1 disposed 45 in an orifice of partition 9, and into bath 4 and under roll I8 immersed therein; thence out of bath 4 between a pair of squeegee rolls I9 of rubber or the like; and thence through an evaporator 20, passing out of the system over a roll 2|.

Pure cleaning liquid is fed into bath 4, preferably continuously, at a properly adjusted ra'te, through an inlet pipe 22. The liquid of bath 4 in turn flows or seeps at about the same rate through and around the felt members I1 in partition 9, into bath l.' The liquid in this bath in turn flows correspondingly into bath 2 over the low barrier separating tanks 5 and 8. Also the liquid of bath 2 flows correspondingly into bath I through and around the felt members I3 in partition I. The liquid of bath I is in turn drawn up at a corresponding rate by an intake line 24 and passed into a purifier and oil separator 25, such as an oil still, the purified cleaner liquid being returned over pipe line 26 to a reservoir 21 from which the outlet'pipe 22 is fed through a control valve 2l. The oil separated from the cleaner liquid in purifier 25 is returned over av pipe line 29 to hot oil bath (not shown) through which the metal strip Il passes as aforesaid prior to' cleaning. In this way a positive flow of the liquid is established between the baths in the direction opposite to that in which the metal strip III is fed.

As cleaning liquid for the baths, such solvents may be used as carbon tetrachloride, trichlorethylene, perchlor-ethylene, cleaners naphtha, etc. 'I'he ilrst of these solvents is preferred owing to its nreproof properties and its low vapor pressure at atmospheric temperature.

In the operation of the system, bath I removes most of the oil and other impurities from the wholly uncleaned strip entering thesame. This bath is, therefore, the most contaminated because of this and because it receives the flow and the impurities therein from all of the other baths. Each `of baths 2, 3 and 4 is in turn progressively cleaner than Ithat preceding, because the strip is cleaner as it enters and because the liquid which flowsinto it comes from a cleaner source, namely, from thepreceding bath in the direction of flow, except for bath 4 which, however, is fed the highly purified cleaner of reservoir 21. As the strip traverses the bath it, therefore, becomes progressively cleaner and traverses progressively cleaner baths until on entering, in a well cleaned condition, bath 4 of high purity, all residual traces of oil, etc. are removed'.

'Ihe vapor level above the baths is kept low by m'eans of the pipes 30 disposed above the baths and within which cold water is circulated.

As the strip passes out of bath 4, the greater portion of the solvent adhering thereto is mechanically removed by passage through the squeegee rolls I9. The solvent remaining on the strip is thereupon removed by evaporation as the strip passes between the plates 3l, 32 heated by steam pipes 33, 34, forming part of the evaporator. Referring to Fig. 2, the solvent thus vaporized flows off laterally to the left and right between a series of cold water pipes 35, 36, which condense the vaporized solvent to the liquid state again out of contact withsthe strip.

To facilitate examination of the apparatus and the strip, the coverfor the baths is made up of a series of` removable plates 31; while the rollers I2, I4, I8, Il, are mounted on pivoted arms 38 amxed to levers whereby the rolls may be swung up to the position indicated by the dotted line What we claim is:

1. Apparatus for cleaning surface contaminated metal strip, which comprises: a plurality of baths containing cleaning liquid and disposed in sequence, feed-roll conveying means for feeding said strip longitudinally in one direction through said baths successively, means for establishing a flow of said liquid between said baths successively and in the direction opposite to that in which the strip is fed, means for cascading said flow between lat least some of said baths, means for removing a portion of the highly contaminated liquid in the first bath of said sequence traversed by said strip, means for purifying the liquid so removed and for returning the purified liquid to the final bath of said sequence traversed by said strip, means for mechanically removing a. portion of the cleaning liquid adhering to said strip upo'n emergence from said baths, means for evaporating to dryness the residual liquid successively and in the direction opposite to that in which the strip is fed, means for cascading said flow between at least some of said baths, means for removing a portion of the highly contaminated liquid in the first bath of said sequence traversed by said strip, means for purifying the liquid so removed and for returning the purified liquid to the nal bath of said sequence traversed by said strip, means for mechanically removing a portion of the cleaning liquid adhering to said strip upon emergence from said baths, means including a pair of heated plates between which the strip is passed, for evaporating to dryness the residual liquid retained on said strip, and condensing means laterally disposed with respect to said heated plates,.for condensing the evaporated liquid out of contact with said strip.

JOHN F. FERM.

EDWARD WILLIAM HOPPER. 

